The methanol binds to the water through van der Waals interactions and hydrogen bonding, lowering the evaporation point of the water resulting in dehydration of the tissue. There is also some osmotic effect going on - the water percent in methanol is usually quite low so the water in the cells gets sucked out to dilute the methanol, leading to further dehydration.

Rehydration has to take places to restore cells to their former size, the dehdration shrinks them.